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Number of partitions of n into parts 4k or 4k+1.
2

%I #16 Jan 27 2019 21:36:15

%S 1,1,1,2,3,3,3,5,7,8,8,11,15,17,18,23,30,35,37,45,57,66,71,84,104,121,

%T 131,151,183,212,231,263,313,362,396,446,523,601,660,738,855,979,1076,

%U 1196,1372,1562,1719,1903,2164,2454,2701,2979,3363,3795,4177,4594

%N Number of partitions of n into parts 4k or 4k+1.

%C Also number of partitions of n such that number of 1's plus number of odd parts is greater than or equal to n. - _Vladeta Jovovic_, Feb 27 2006

%F G.f.: -1 + 1/((1-x)*Product_{j>=1} (1-x^(4j))*(1-x^(4j+1))). - _Emeric Deutsch_, Mar 07 2006

%F a(n) ~ exp(Pi*sqrt(n/3)) * Gamma(5/4) / (2^(1/4) * 3^(3/8) * Pi^(3/4) * n^(7/8)). - _Vaclav Kotesovec_, Aug 27 2015

%e a(8)=5 because we have [8],[5,1,1,1],[4,4],[4,1,1,1,1] and [1,1,1,1,1,1,1,1].

%p g:=-1+1/(1-x)/product((1-x^(4*j))*(1-x^(4*j+1)),j=1..20): gser:=series(g,x=0,60): seq(coeff(gser,x^n),n=1..56); # _Emeric Deutsch_, Mar 07 2006

%t nmax = 100; Rest[CoefficientList[Series[Product[1/((1 - x^(4k+4))*(1 - x^(4k+1))), {k, 0, nmax}], {x, 0, nmax}], x]] (* _Vaclav Kotesovec_, Aug 27 2015 *)

%K nonn

%O 1,4

%A _Olivier GĂ©rard_